Studies On The Mechanisms Of Genetic Instability Involving In The Process Of α Particles Radiation Carcinogenesis

Carcinogenesis is one of the major biological effects induced by ionizing radiation. a particle emitting isotopes are now widely used in the nuclear industries, could even be used by the terrorisms to construct the DDR or dirty bomb. A number of epidemiological studies indicate that radon is an important environmental factor that is associated with the development of human bronchogenic carcinoma. Although the close association between radon exposure and lung cancer has been revealed, the detailed mechanisms of radon-induced lung cancer are still unclear.Cell cycle checkpoints and DNA repair are thought to be essential for ensuring the genome or chromosomes integrity. Current study was to investigate the changes of cell cycle checkpoints, DNA repair and disrupted spindle-induced apoptotic responsiveness in the malignant transformed cell lines of human bronchial epithelial BEP2D cells generated by a particle exposure. The results were summarized below:1) Tumor cells were isolated from nude mice generated by implanting passage 35 cells of a -particles-irradiated BEP2D cells and were subcloned in vitro. Five individual malignant transformed cell lines named as BERP35T-1 / -2 / -4 / -5 / -6 were subcloned. The malignant transformed phenotype was further manifested by cellular morphological changes, increased cell growth, cytogenetic changes, etc.2) The cytogenetic characteristics of five individual malignant transformed cell lines were analyzed. Deletions of one copy of chr13 and chrY, and an unidentified fragment attached on the long arms of chr2 and chr12 respectively were observed in all the malignant transformed cell lines. The ratio of polyploids of BERP35T-4 cells was about 40.0 % at passage 5 and enhanced to 65%, significant higher than that of PEB2D cells.3) Transformed cell lines BERP35T1 and BERP35T4 showed a markedly lower capacity of v -ray-induced DNA DSBs rejoining and highly increasedradiosensitivity than parental BEP2D cells. The analysis of gene express (mRNA) level by DNA microarray, RT-PCR and Northern blot hybridization revealed a significant depressed expression of the DNA repair genes XRCC-2?XRCC-3? XRCC-5?ERCC-2?ERCC4?EXO1?APEX?UNG?NBS1?NTHL1 in the malignant transformed cells. However, an increased expression was detected in transformed BERP35T4 cells as well as in human non small lung cancer tissues and in hepato- and cholangio- neoplasm.4) The mitotic spindle checkpoint and apoptosis in response to nocodazole, a microtubule-disrupting agent, were investigated in a particles-transformed human bronchial epithelial cell lines BERP35T1, BERP35T4 and the parental BEP2D cells. When treated with 0.2ug/ml of nocodazole, BEP2D and BERP35T1 cells were efficiently arrested in mitotic phase, whilst BERP35T4, a transformed cell line showing chromosomal instability, failed to arrest, and demonstrated a low G2/M fraction and a high aneuploidy ratio, indicating that BERP35T4 cells has an defect in spindle checkpoint function. Methylation of 5'CpG island of Chfr gene, a mitotic checkpoint gene that functions in early prophase to delay chromosome condensation, was found in BERP35T4 cell but not in BEP2D cells. As coincident with methylation status, the expression of Chfr gene was markedly suppressed.5) The extent of apoptosis induced by nocodazole (0.3ug/ml) was significantly higher (2~2.5 fold) in BEP2D cells than that in two transformed cell lines. Furthermore, the apoptosis was found to take place dominantly before mitotic division in BEP2D cells but half of them after mitotic division in BERP35T4 cells, the later was characteristic of increased ratio of dinucleated apoptotic cells when co-treated with cytochalsin B.